The present invention relates to a yarn withdrawal navel for an open-end spinning apparatus, which yarn withdrawal navel is provided with a ferromagnetic locating surface for the purpose of coupling it to a mounting, said mounting comprising at least one permanent magnet.
A known yarn withdrawal navel of this kind (U.S. Pat. No. 4,110,961) is connected with a mounting comprising a yarn withdrawal duct and is exchangeable by means of magnetic coupling means. The yarn withdrawal navel itself can be of ferromagnetic material or it can be made from ceramic material with a ferromagnetic ring. In order to replace the yarn withdrawal navel, a tool in the shape of a supplementary magnet is used, whose magnetic force is either inverse to the force of the permanent magnet or else exceeds it.
A further known yarn withdrawal navel (U.S. Pat. No. 4,854,119) is made of ceramic material and has a ferromagnetic disk on the side facing the mounting, which disk has the same diameter as the yarn withdrawal navel. A permanent magnet in the shape of a flat ring disk is affixed to the mounting, the ring disk, having the same diameter as the ferromagnetic disk. The ring disk is recessed over a sector of approximately 60.degree., so that a fiber feed channel can be guided past at this point. The yarn withdrawal navel is centered with a tube-like extension in a bore hole of the permanent magnet. The publication contains no information as to how the magnetic coupling is released.
Yarn withdrawal navels capable of being coupled to mountings by magnetism have the advantage of taking up less space, as, for example, the fastening thread usually present is eliminated. Due to the elimination of the thread, a mounting made of plastic can be used. In the case of the two known yarn withdrawal navels, there are, however, no restrictions with respect to their assembly position as to the yarn axis. In some cases, however, a preferred assembly position of the yarn withdrawal navel is desirable, for example when the yarn withdrawal navel has an asymmetrical form.
An object of the present invention is to guarantee a desired assembly position in the case of a yarn withdrawal navel capable of being coupled to a mounting by magnetism and furthermore preferably to facilitate the releasing of the magnetic coupling.
This object has been achieved in accordance with the present invention by applying a positioning means to the yarn withdrawal navel which at least weakens the magnetic force on the locating surface at another assembly position of the yarn withdrawal navel other than the designated one.
Due to the features of the invention, the yarn withdrawal navel partakes in the securing of the correct assembly position. Only in the case of a particular embodiment of the yarn withdrawal navel in combination with a particular assembly position is the yarn withdrawal sufficiently magnetically secured on the mounting.
Preferably the positioning means comprises a holding notch which secures the assembly position. The respective assembly position is thus set exactly as a result of such an interlocking device.
In a particularly favorable embodiment, a positioning means in the form of a de-coupling device is used, which de-coupling device weakens or cancels the magnetic effect when the yarn withdrawal navel is turned. This means that the yarn withdrawal navel is only coupled to the mounting in a predetermined rotational position in relation to the yarn axis. The magnetic force is reduced when the yarn withdrawal navel is turned around the yarn axis. This results, in addition to the securing of a correct assembly position, in an easier releasing of the magnetic coupling when the yarn withdrawal navel is dismounted.
The decoupling device according to certain preferred embodiments comprises at least one recess in the locating surface, to which recess the permanent magnet can be disposed. By turning the yarn withdrawal navel, and therefore the ferromagnetic locating surface, around the yarn axis, the recess is pushed over the permanent magnet, whereby the magnetic force of attraction on the locating surface is lifted so that the yarn withdrawal navel can be easily dismounted. Turning can be effected, if desired, by means of a tool.
In another embodiment, the de-coupling device comprises at least one supporting surface which raises the locating surface from the mounting. When the yarn withdrawal navel is turned around the yarn axis, the ferromagnetic locating surface lifts itself off the permanent magnet. This variation has the additional advantage in that single magnets do not have to be used; if desired, a ring magnet can be used.
The yarn withdrawal navel does not have to be made completely from a ferromagnetic material, for example from steel, but can be made of a ceramic material connected to a steel ring.
These and further objects, features and advantages of the present invention will become more readily apparent from the following detailed description thereof when taken in conjunction with the accompanying drawings